The surname Onesti is of anthroponymic origin and derives from the medieval name Onesto (from the Latin Honestus or Onestus), used with the meaning "worthy" or "endowed with noble sentiments". On this point E. De Felice and F. De Laurentiis agree, highlighting its moral value in the medieval context, where the name functioned as an expression of virtue and honourableness.

Along the same lines, E. Rossoni confirms this origin from documented Latin forms and notes that the surname may have been formed directly from the name or through variants and diminutives. He further supplies historical testimonies —such as the mention of Onestus in a parchment of 1254 at Perugia— that evidence its use in the medieval period, as well as the existence of different forms derived from the same name, all linked to the same root and meaning.